Fluorine-containing olefinic monomers, in particular tetrafluoroethylene (which is hereinafter referred to as "TFE") and chloro-trifluoroethylene (which is hereinafter referred to as "CTFE") are industrially important chemicals as a starting material for the production of a polymer of such a single monomer or a copolymer of such a monomer with another monomer or as an intermediate product for the production of various chemicals. Since TFE and CTFE have so low boiling points as -76.3.degree. C. and -27.9.degree. C. respectively, they are usually stored under pressure. Because of their high reactivities, they are ready to polymerize even in the presence of a trace amount of oxygen. In order to prevent such polymerization of the monomer during its storage, it has been known that a polymerization inhibitor (polymerization preventive agent) is added to the monomer (see, for example, U.S. Pat. No. 2,407,405).
As such a polymerization inhibitor, terpene compounds such as dipentene, terpinolene, p-cymene, .alpha.-pinene, p-menthane and so on are concretely exemplified. Because of easy handling and commercial availability, a mixture of such terpene compounds is usually used. A composition of a terpene polymerization inhibitor mixture is shown in Table 1 below which is commercially available:
TABLE 1 ______________________________________ Component Product A Product B Product C ______________________________________ .alpha.-pinene 4.0% 5.0% 3.1% camphene 3.6 3.6 3.4 .beta.-pinene 1.3 0.2 0.5 .alpha.-terpinene 28.4 29.5 29.8 dipentene 14.6 11.4 18.5 .gamma.-terpinene 16.6 17.5 14.9 isoterpinolene 12.7 9.6 7.9 terpinolene 6.4 13.8 10.6 others 12.4 4.0 11.3 ______________________________________ Product A: Terpene mixture commercially available from ArakawaChemial as trade name of TerpeneB Product B: Terpene mixture commercially available from NipponTerpene as trade name of DipentenT Product C: Terpene mixture commercially available from YasuharaYushi as trade name of Dipenten
In order to use the stored monomer for a certain intended object such as polymerization thereof, it is required to remove the polymerization inhibitor of the terpenes which has been added to the monomer. For example, the monomer must be separated from the polymerization inhibitor and purified by treatment such as distillation, absorption or adsorption (for example, adsorption with silica gel). In such a case, if the separation of the polymerization inhibitor is insufficient or if a remaining amount of the polymerization inhibitor in the monomer fluctuates, the following disadvantages occur upon the polymerization of the monomer: consumption increase of a polymerization initiator, polymerization period increase due to reduction of polymerization reaction rate, decrease of polymer yield and property fluctuation of produced polymer. Therefore, the monomer is used as, for example, a polymerization starting material after the polymerization inhibitor has been removed from the monomer by a multistage separation-purification.
For the production of a polymer from a single kind monomer or a copolymer comprising the monomer, it is firstly desired to make a monomer quality uniform from a viewpoint of polymerization stability while polymerization conditions (in particular, a pressure and a temperature of a polymerization vessel) should be controlled and thus polymer property uniformity of the resulted polymer should be intended.
The fluorine-containing monomer is introduced into a polymerization vessel generally in a gas form for the polymerization thereof. For composition analysis of the gas monomer, a gas chromatography (which is hereinafter referred to as GC) is generally used. However, even though a flame ionization detector (which is hereinafter referred to as FID) providing the best sensitivity for the analysis of hydrocarbonaceous organic compounds is employed, a detection lower limit of terpenes as whole is about a few ppm for the case in which the polymerization inhibitor to be analyzed is a mixture of isomers as a terpene mixture since each compound of the terpenes is of a low concentration in spite that a concentration of the total terpenes is relatively large.
Generally, a concentration of the terpenes as a whole and also a concentration of each terpene compound in the monomer for the polymerization must be considerably lower than the detection lower limit of the GC with the FID after it has been purified, and it is therefore impossible to control a quality of a feedstock with the concentration of the remaining polymerization inhibitor in the feedstock using the GC. So the remaining polymerization inhibitor in a trace amount affects a polymerization step of the monomer, which is one of reasons why polymerization conditions are not stabilized. Although extensive maintenance and control of the polymerization step have been carried out from various viewpoints, they have not overcome the problems such as the fluctuation of the produced polymer properties.